What is a strut and shock absorber?

A car’s suspension system uses a shock absorber and struts to maintain tyre traction with the road, absorb bumps and avoid body roll around corners. If the car is not able to keep the tyres in contact with the road surface, it may lead to handling issues, loss of control, uneven tyre wear and problems with acceleration and braking.

What are the functions of shock absorbers and struts?

Shock absorbers and struts are used to:

  •       Keep the body and wheels stable
  •       Prevent the car from bouncing and swaying
  •       Brake dive and acceleration squat are prevented
  •       The car can handle well and ride quality is good
  •       Maintain alignment of tyres
  •       Premature wear and tear of tyres and suspension is prevented

Shock absorbers vs struts

The words shock absorber and strut do not refer to the same suspension component. They are two different parts that have their own functions. Shocks and struts both help in the dynamics of the vehicle, but shock absorbers are individual components of the suspension system while struts are a structural part of the chassis and suspension.

Shock absorbers working and principles

Shocks do not support the car’s weight instead they control the suspension movement. They absorb bumps in the road by converting kinetic energy into thermal energy. Shock absorbers are filled with hydraulic fluid (oil) for this energy conversion and damping.

The shock absorber provides resistance to the movement of the suspension through the use of a piston that has holes in it. The holes in the piston allow the oil to flow through it and slow down the bouncing movement of the suspension.

The shocks are able to provide more resistance with increased movement of the suspension. Shock’s main functions include:

  •       Reducing the bounce factor of the vehicle
  •       Preventing roll and sway as the vehicle turns corners
  •       Absorbing impact and adjusting weight transfer of the vehicle
  •       Damping brake dive and acceleration squat

Shock absorbers have a hydraulic fluid that slows down movement during its compression and extension functions. A compressed shock absorber controls the unsprung weight of the vehicle by resisting extension movements of the shock absorber.

Also Read: What are performance tyres?

What components does a shock absorber have?

A shock absorber can basically be described as an oil pump. The hydraulic fluid (oil) works against the compression of the piston in the pressure tube.

When the shock absorber is compressed, the piston is forced against the oil. The hydraulic fluid (oil) moves through holes in the piston. Therefore the piston slows down and causes damping of the bumps in the road.

As the piston is resisting the force through it, it slows down the spring and suspension movement.

Why does a suspension system use struts?

The suspension uses a strut as a damping system in the front and sometimes in the rear of the car. This is a type of independent suspension. Each wheel has the ability to move without affecting the other wheels.

The strut is part of the upper arm of the suspension and forms a structural part of it. Struts are lighter than shock absorbers and occupy less space in a suspension set-up.

There are two main functions of a strut. One is performing a damping function similar to the shock absorber. It has a piston within a cylinder and a piston rod that pushes against hydraulic fluid to control the up and down movement of the spring and suspension.

Struts provide resistance to the kinetic energy of the suspension. It is also velocity-sensitive just like the shock absorber which means it can increase or decrease the amount of resistance depending on how fast the suspension moves up or down.

The second function of the strut is to provide a structural component to the suspension. There is a coil spring over the strut, and it holds the wheel in place keeping it well aligned. They also provide structural support for side load and lead to affecting the ride and handling, steering, braking and wheel alignment.

What components does a strut have?

The strut housing provides structural support for the suspension assembly and has a coil over the spring on top of the strut. Struts connect to the steering knuckle at the bottom end which connects to the lower arm.

The strut consists of a strut housing, damping unit with a coil spring around it to support the weight of the vehicle.

Does car suspension use struts or shocks?

Every wheel of the vehicle either has a shock absorber or a strut to soak up bumps on the road. Some cars have shock absorbers at the front and struts at the rear or vice versa. Each wheel has some sort of ride control component.


This article outlines the working and main differences between a shock absorber and a strut. If you found this article interesting, you may want to read about the difference between petrol and diesel engine.